Let me clear all your queries.
1) What is this steermatic City?
Ans. Steermatic City was a variant of last model City launched in 2008. It had a 1.5L engine, 7speed CVT-i transmission and sort of paddle shiftters.
2) More cc in car engine means more power and more fuel I guess?
It doesn't mean that. A car should have a proper power:weight ratio for good performance and fuel economy. A car like new Corolla with tiny 1.3L engine will never deliever satisfactory performance and economy, b'coz It's power:weight ratio is not proper (unstable).
3) Is It possible that a car of 2008 has run under 50,000km?
Ans. Yes, It is possible. My Chevrolet Joy has just ran 55,000KM, It was bought in 2009.
4) A 2008 steermatic car in ISB on PW, KHI reg is being sold under 11 Lakh. I would expect 1500cc to be around 15 Lakh, is there a catch in this?
Ans. No, there is no catch in It. In ISB a steermatic should cost maximum 1150K, that shoud be in a good nick.
5) I see it's 1500cc, will it still give good average so that I can manage in 200L a month?
Ans. You drive 100KM a day? Let's calculate.
You can afford 22-24K fuel in a month.
A steermatic gives 11-12 KM/Liter and on highways It gives 13-14 KM/Liter.
Let's take 13KM/Liter as average.
100KM/13KM = 7.692 Liters (You will use 7.692 liters per day as per my calculation)
200 liters/7.692 = 26 days.
With 200 liters and 7.692 or less liters consumption per day. You'll have fuel for 26 days.
But It depends, If you are a calm driver then the car would deliever you more.
Steermatic has a much better performance and transmission than IDSI, the CVT-i in steermatic is meant for economy as well.
While the IDSI is purely meant for economy, you'll never enjoy driving It.
Conclusion:
It depends on you, If you can afford Steermatic and It's economy then I'll surely recommend you to go for It.
IDSI was the slowest 1.3L in Pakistan. It was purely made for economy. You will never enjoy driving It. But you will have some savings.